The Quadratus lumborum is a muscle in the lower back. It is irregular and quadrilateral
in shape, and broader below than above.
Structure It originates from the lower border of the
last rib for about half its length, and by four small tendons from the apices of the
transverse processes of the upper four lumbar vertebrae. It inserts via aponeurotic fibers
into the iliolumbar ligament and the internal lip of the iliac crest for about 5 cm.,
Occasionally a second portion of this muscle is found in front of the preceding. It arises
from the upper borders of the transverse processes of the lower three or four lumbar vertebræ,
and is inserted into the lower margin of the last rib.
Relations Anterior to the Quadratus lumborum are the
colon, the kidney, the Psoas major and psoas minor, and the diaphragm; between the fascia
and the muscle are the twelfth thoracic, ilioinguinal, and iliohypogastric nerves.
Variations The number of attachments to the vertebræ
and the extent of its attachment to the last rib vary.
Functions The quadratus lumborum can perform four actions:
Lateral flexion of vertebral column, with ipsilateral contraction
Extension of lumbar vertebral column, with bilateral contraction
Fixes the 12th rib during forced expiration Elevates the Ilium, with ipsilateral contraction
Clinical significance Back pain
The quadratus lumborum, or QL, is a common source of lower back pain. Because the QL
connects the pelvis to the spine and is therefore capable of extending the lower back when contracting
bilaterally, the two QLs pick up the slack, as it were, when the lower fibers of the erector
spinae are weak or inhibited. Given their comparable mechanical disadvantage, constant
contraction while seated can overuse the QLs, resulting in muscle fatigue. A constantly
contracted QL, like any other muscle, will experience decreased blood flow, and, in time,
adhesions in the muscle and fascia may develop, the end point of which is muscle spasm.
This chain of events can be and often is accelerated by kyphosis, which is invariably accompanied
by rounded shoulders, both of which place greater stress on the QLs by shifting body
weight forward, forcing the erector spinae, QLs, multifidi, and especially the levator
scapulae to work harder in both seated and standing positions to maintain an erect torso
and neck. The experience of "productive pain" or pleasure by a patient upon palpation of
the QL is indicative of such a condition. Hip abduction is performed primarily by the
hip abductors. When the gluteus medius/minimus are weak or inhibited, the TFL or QL will
compensate by becoming the prime mover. The most impaired movement pattern of hip abduction
is when the QL initiates the movement, which results in hip hiking during swing phase of
gait. Hip hiking places excessive side-bending compressive stresses on the lumbar segments.
Thus, a tight QL may be another hidden cause of low back pain.
When the hip adductors are tight or hypertonic, their antagonist may experience reciprocal
inhibition. The gluteus medius will become weak and inhibited. This in turn may cause
hypertonicity of ipsilateral QL. Chronic hypertonicity of QL tends to cause low back pain due to
its ability to create compressive stress on lumbar segment. Current studies show that
application of heat or ice, massage, and estim will not leave long-term benefits. Careful
assessment of muscular imbalances and movement impairments by a therapist is recommended
in order to address the underlying issues mentioned.
While stretching and strengthening the QL are indicated for unilateral lower back pain,
heat or ice applications as well as massage should be considered as part of any comprehensive
rehabilitation regimen. Additional images
References This article incorporates text from a public
domain edition of Gray's Anatomy.
External links Origin, insertion and nerve supply of the
muscle at Loyola University Chicago Stritch School of Medicine
-1234501552 at GPnotebook quadratus+lumborum+muscle at eMedicine Dictionary
Atlas image: abdo_wall70 at the University of Michigan Health System - "Posterior Abdominal
Wall, Dissection, Anterior View"